Continuously variable transmission

ABSTRACT

Components, subassemblies, systems, and/or methods for continuously variable transmissions (CVT) having a control system adapted to facilitate a change in the ratio of a CVT are described. In one embodiment, a control system includes a stator plate configured to have a plurality of radially offset slots. Various traction planet assemblies and stator plates can be used to facilitate shifting the ratio of a CVT. In some embodiments, the traction planet assemblies include planet axles configured to cooperate with the stator plate. In one embodiment, the stator plate is configured to rotate and apply a skew condition to each of the planet axles. In some embodiments, a stator driver is operably coupled to the stator plate. Embodiments of a traction sun are adapted to cooperate with other components of the CVT to support operation and/or functionality of the CVT.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/198,402, filed Aug. 26, 2008. The disclosures of all of theabove-referenced prior applications, publication, and patents areconsidered part of the disclosure of this application, and areincorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention relates generally to transmissions, and moreparticularly to methods, assemblies, and components for continuouslyvariable transmissions (CVTs).

2. Description of the Related Art

There are well-known ways to achieve continuously variable ratios ofinput speed to output speed. Typically, a mechanism for adjusting thespeed ratio of an output speed to an input speed in a CVT is known as avariator. In a belt-type CVT, the variator consists of two adjustablepulleys coupled by a belt. The variator in a single cavity toroidal-typeCVT usually has two partially toroidal transmission discs rotating abouta shaft and two or more disc-shaped power rollers rotating on respectiveaxes that are perpendicular to the shaft and clamped between the inputand output transmission discs. Usually, a control system is used for thevariator so that the desired speed ratio can be achieved in operation.

Embodiments of the variator disclosed here are of the spherical-typevariator utilizing spherical speed adjusters (also known as poweradjusters, balls, planets, sphere gears, or rollers) that each has atillable axis of rotation adapted to be adjusted to achieve a desiredratio of output speed to input speed during operation. The speedadjusters are angularly distributed in a plane perpendicular to alongitudinal axis of a CVT. The speed adjusters are contacted on oneside by an input disc and on the other side by an output disc, one orboth of which apply a clamping contact force to the rollers fortransmission of torque. The input disc applies input torque at an inputrotational speed to the speed adjusters. As the speed adjusters rotateabout their own axes, the speed adjusters transmit the torque to theoutput disc. The output speed to input speed ratio is a function of theradii of the contact points of the input and output discs to the axes ofthe speed adjusters. Tilting the axes of the speed adjusters withrespect to the axis of the variator adjusts the speed ratio.

There is a continuing need in the industry for variators and controlsystems therefor that provide improved performance and operationalcontrol. Embodiments of the systems and methods disclosed here addresssaid need.

SUMMARY OF THE INVENTION

The systems and methods herein described have several features, nosingle one of which is solely responsible for its desirable attributes.Without limiting the scope as expressed by the claims that follow, itsmore prominent features will now be discussed briefly. After consideringthis discussion, and particularly after reading the section entitled“Detailed Description of Certain Inventive Embodiments” one willunderstand how the features of the system and methods provide severaladvantages over traditional systems and methods.

One aspect of the invention relates to a method of adjusting a speedratio of a continuously variable transmission (CVT) having a group oftraction planets. Each traction planet has a tiltable axis of rotation.The method includes the step of configuring a stator of the CVT to applya skew condition to each tiltable axis of rotation independently. In oneembodiment, the skew condition is based at least in part on an angulardisplacement of the stator plate. In another embodiment, the skewcondition is based at least in part on a tilt angle of the tiltable axisof rotation.

Another aspect of the invention concerns a method of adjusting a speedratio of a continuously variable transmission (CVT) that has a group oftraction planets. Each traction planet has a tiltable axis of rotation.In one embodiment, the method includes the step of rotating a stator towhich each traction planet is operably coupled. The stator can beconfigured to independently apply a skew condition to each tiltable axisof rotation. The method can also include the step of guiding eachtiltable axis of rotation to an equilibrium condition. The equilibriumcondition can be based at least in part on the rotation of the statorplate. In some embodiments, the equilibrium condition substantially hasa zero-skew angle condition.

Yet another aspect of the invention concerns a method of supporting agroup of traction planets of a continuously variable transmission (CVT).Each traction planet has a tiltable axis of rotation. In one embodiment,the method includes the step of providing a first stator plate having anumber of radially offset slots. The radially offset slots are arrangedangularly about a center of the first stator plate. The method caninclude the step of operably coupling each of the traction planets tothe first stator plate. In one embodiment, the method includes the stepof providing a second stator plate having a number of radial slots. Theradial slots can be arranged angularly about the center of the secondstator plate. The method can also include the step of operably couplingthe traction planets to the second stator plate.

One aspect of the invention concerns a method of adjusting a speed ratioof a continuously variable transmission (CVT) that has a group oftraction planets. Each traction planet has a tiltable axis of rotation.The method includes the step of providing a stator plate operablycoupled to each of the traction planets. In one embodiment, the methodincludes the step of receiving a set point for a speed ratio of the CVT.The method can include the step of determining a set point for anangular displacement of the stator plate. The set point can be based atleast in part on the set point for the speed ratio. The method can alsoinclude the step of rotating the stator plate to the set point for theangular displacement of the stator plate. Rotating the stator plate caninduce a skew condition on each tiltable axis of rotation. The statorplate can be configured to adjust the skew condition as each tiltableaxis of rotation tilts.

Another aspect of the invention concerns a method of adjusting a speedratio of a continuously variable transmission (CVT) that has a group oftraction planets. Each traction planet can be configured to have atiltable axis of rotation. The method can include the step ofdetermining a set point for a speed ratio of the CVT. In one embodiment,the method can include the step of measuring an actual speed ratio ofthe CVT. The method includes the step of comparing the actual speedratio to the set point for the speed ratio to thereby generate acomparison value. The method also includes the step of rotating a statorplate to an angular displacement based at least in part on thecomparison value. Rotating the stator plate applies a skew condition toeach of the traction planets. The skew condition changes as eachtiltable axis of rotation tilts and the angular displacement remainsconstant.

Yet one more aspect of the invention addresses a continuously variabletransmission (CVT) that has a group of traction planets arrangedangularly about a main drive axis. Each traction planet has a tiltableaxis of rotation. The CVT has a first stator plate that is coaxial withthe main drive axis. The first stator plate can have a number ofradially offset slots. The radially offset slots can be configured suchthat each tiltable axis is guided independently from the others. The CVTcan have a second stator plate coaxial with the main drive axis. Thesecond stator plate can have a number of radial slots. The radial slotscan be configured to independently guide the tiltable axes of rotation.The first stator plate is configured to rotate relative to the secondstator plate.

In another aspect, the invention concerns a stator plate for acontinuously variable transmission (CVT) that has a number of tractionplanets. The stator plate can have a substantially disc shaped bodyhaving a center. In one embodiment, the stator plate can have a numberof radially offset guides arranged angularly about the center. Each ofthe radially offset guides can have a linear offset from a centerline ofthe disc shaped body.

Another aspect of the invention relates to a continuously variabletransmission (CVT) that has a group of traction planets. Each tractionplanet has a tiltable axis of rotation. In one embodiment, the CVT has afirst stator plate arranged coaxial about a main drive axis of the CVT.The first stator plate can be operably coupled to each traction planet.The first stator plate can have a number of radially offset slotsarranged angularly about a center of the first stator plate. Each of theradially offset slots can have a linear offset from a centerline of thefirst stator plate. The CVT can also have a second stator plate arrangedcoaxial about a main drive axis of the CVT. The second stator plate hasa number of radial slots. The radial slots can be arranged angularlyabout a center of the second stator plate. Each of the radial slots issubstantially radially aligned with the center of the second statorplate. The CVT can have an actuator operably coupled to at least one ofthe first and second stator plates. The actuator can be configured toimpart a relative rotation between the first and second stator plates.

One aspect of the invention relates to a ball planetary continuouslyvariable transmission (CVT) that includes a group of traction planets.Each traction planet has a tiltable axis of rotation. The CVT can alsoinclude a first guide aligned with a line perpendicular to a main driveaxis of the CVT. The first guide can be configured to act upon thetiltable axis of rotation. The CVT can also include a second guidealigned with a line that is parallel to the line perpendicular to themain drive axis of the CVT. The second guide can be configured to actupon the tiltable axis of rotation.

Another aspect of the invention concerns a method of manufacturing acontinuously variable transmission (CVT). In one embodiment, the methodincludes the step of providing a first guide radially aligned with aline perpendicular to a main drive axis of the CVT. The method includesthe step of providing a second guide offset. On a projection plane,respective projection lines of the first and second guides intersectthereby forming an intersection location. The method can include thestep of operably coupling a group of traction planets to the first andsecond guides. The method can also include the step of configuring thefirst and second guides such that they are capable of rotation relativeto one another about the main drive axis.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a schematic diagram of certain components of a ball planetarycontinuously variable transmission (CVT) and certain relevant coordinatesystems.

FIG. 1B is a diagram of certain relative-coordinate systems related to acoordinate system shown in FIG. 1A.

FIG. 1C is a schematic diagram of certain kinematic relationshipsbetween certain contacting components of the CVT of FIG. 1A.

FIG. 1D is a representative chart of traction coefficient versusrelative velocity for a typical traction fluid and rolling contactbetween CVT traction components.

FIG. 1E is a free body diagram of a traction planet of the CVT of FIG.1A.

FIG. 1F is a schematic diagram of a traction planet of the CVT of FIG.1A showing a skew angle.

FIG. 2 is a block diagram of an embodiment of a drive apparatusconfigured to use certain inventive embodiments of CVTs and skew controlsystems and methods therefor disclosed here.

FIG. 3 is a schematic diagram of certain components of a ball planetaryCVT and certain relevant coordinate systems.

FIG. 4 is a schematic diagram of certain components of the CVT of FIG. 3and certain relevant coordinate systems.

FIG. 5A is a schematic diagram of certain components of the CVT of FIG.3.

FIG. 5B is a schematic diagram of certain components of the CVT of FIG.3.

FIG. 5C is a schematic diagram of certain components that can be usedwith the CVT of FIG. 3.

FIG. 6A is a flow chart of a skew-based control process that can be usedwith the CVT of FIG. 3.

FIG. 6B is a chart representing a look-up table that can be used in asubprocess of the skew-based control process of FIG. 6A.

FIG. 6C is a flow chart of an actuator subprocess that can be used withthe skew-based control process of FIG. 6A.

FIG. 7 is a cross-sectional view of an inventive embodiment of a CVThaving a skew control system.

FIG. 8 is a cross-sectional view of another inventive embodiment of aCVT having a skew control system.

FIG. 9 is a cross-sectioned, partial perspective view of the CVT of FIG.7.

FIG. 10 is a plan view depicting certain components of the CVT of FIG.7.

FIG. 11A is a plan view of an inventive embodiment of a stator platethat can be used with the CVT of FIG. 7.

FIG. 11B is a perspective view of the stator plate of FIG. 11A.

FIG. 12 is a cross-section view A-A of the stator plate of FIG. 11A.

FIG. 13 is a cross-section view B-B of the stator plate of FIG. 11A.

FIG. 14 is a plan view of another embodiment of a stator plate that canbe used with the CVT of FIG. 3.

FIG. 15 is a cross-sectional view of the stator plate of FIG. 14.

FIG. 16 is an exploded, perspective view of a traction planetsubassembly that can be used with the CVT of FIG. 6.

FIG. 17 is an exploded, perspective view of another embodiment of atraction planet subassembly that can be used with the CVT of FIG. 6.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

The preferred embodiments will be described now with reference to theaccompanying figures, wherein like numerals refer to like elementsthroughout. The terminology used in the descriptions below is not to beinterpreted in any limited or restrictive manner simply because it isused in conjunction with detailed descriptions of certain specificembodiments of the invention. Furthermore, embodiments of the inventioncan include several inventive features, no single one of which is solelyresponsible for its desirable attributes or which is essential topracticing the inventions described. Certain CVT embodiments describedhere are generally related to the type disclosed in U.S. Pat. Nos.6,241,636; 6,419,608; 6,689,012; 7,011,600; 7,166,052; U.S. patentapplication Ser. No. 11/243,484 and Ser. No. 11/543,311; and PatentCooperation Treaty patent applications PCT/IB2006/054911 andPCT/US2007/023315. The entire disclosure of each of these patents andpatent applications is hereby incorporated herein by reference.

As used here, the terms “operationally connected,” “operationallycoupled”, “operationally linked”, “operably connected”, “operablycoupled”, “operably linked,” and like terms, refer to a relationship(mechanical, linkage, coupling, etc.) between elements whereby operationof one element results in a corresponding, following, or simultaneousoperation or actuation of a second element. It is noted that in usingsaid terms to describe inventive embodiments, specific structures ormechanisms that link or couple the elements are typically described.However, unless otherwise specifically stated, when one of said terms isused, the term indicates that the actual linkage or coupling may take avariety of forms, which in certain instances will be readily apparent toa person of ordinary skill in the relevant technology.

For description purposes, the term “radial” is used here to indicate adirection or position that is perpendicular relative to a longitudinalaxis of a transmission or variator. The term “axial” as used here refersto a direction or position along an axis that is parallel to a main orlongitudinal axis of a transmission or variator. For clarity andconciseness, at times similar components labeled similarly (for example,bearing 1011A and bearing 1011B) will be referred to collectively by asingle label (for example, bearing 1011).

It should be noted that reference herein to “traction” does not excludeapplications where the dominant or exclusive mode of power transfer isthrough “friction.” Without attempting to establish a categoricaldifference between traction and friction drives here, generally thesemay be understood as different regimes of power transfer. Tractiondrives usually involve the transfer of power between two elements byshear forces in a thin fluid layer trapped between the elements. Thefluids used in these applications usually exhibit traction coefficientsgreater than conventional mineral oils. The traction coefficient (μ)represents the maximum available traction forces which would beavailable at the interfaces of the contacting components and is ameasure of the maximum available drive torque. Typically, frictiondrives generally relate to transferring power between two elements byfrictional forces between the elements. For the purposes of thisdisclosure, it should be understood that the CVTs described here mayoperate in both tractive and frictional applications. For example, inthe embodiment where a CVT is used for a bicycle application, the CVTcan operate at times as a friction drive and at other times as atraction drive, depending on the torque and speed conditions presentduring operation.

Embodiments of the invention disclosed here are related to the controlof a variator and/or a CVT using generally spherical planets each havinga tiltable axis of rotation (hereinafter “planet axis of rotation”) thatcan be adjusted to achieve a desired ratio of input speed to outputspeed during operation. In some embodiments, adjustment of said axis ofrotation involves angular misalignment of the planet axis in one planein order to achieve an angular adjustment of the planet axis of rotationin a second plane, thereby adjusting the speed ratio of the variator.The angular misalignment in the first plane is referred to here as“skew” or “skew angle”. In one embodiment, a control system coordinatesthe use of a skew angle to generate forces between certain contactingcomponents in the variator that will tilt the planet axis of rotation.The tilting of the planet axis of rotation adjusts the speed ratio ofthe variator. In the description that follows, a coordinate system isestablished with respect to a spherical traction planet, followed by adiscussion of certain kinematic relationships between contactingcomponents that generate forces which tend to cause the planet axis ofrotation to tilt in the presence of a skew angle. Embodiments of skewcontrol systems for attaining a desired speed ratio of a variator willbe discussed.

Turning now to FIGS. 1A and 1B, coordinate systems will be defined inreference to embodiments of certain components of a continuouslyvariable transmission (CVT). The coordinate systems are shown here forillustrative purposes and should not be construed as the only frame ofreference applicable to the embodiments discussed here. An embodiment ofa CVT 100 includes generally spherical traction planets 108 in contactwith a traction sun 110 (which is schematically shown as a line). Thetraction planets 108 are also in contact with a first traction ring 102and a second traction ring 104 at, respectively, a first angularposition 112 and a second angular position 114. A global coordinatesystem 150 (that is, x_(g), y_(g), z_(g)) and a planet-centeredcoordinate system 160 (that is, x, y, z) are defined in FIG. 1A. Theglobal coordinate system 150 is generally oriented with respect to alongitudinal axis or main drive axis 152 of the CVT 100, for examplewith the z_(g)-axis coinciding with a main drive axis 152 about whichthe traction planets 108 are arranged. The planet-centered coordinatesystem 160 has its origin at the geometric center of the traction planet108, with the y-axis generally perpendicular to the main drive axis 152,and the z-axis generally parallel to the main drive axis 152. Each ofthe traction planets 108 has a planet axis of rotation, that is, aplanet axis 106, which can be configured to rotate about the x-axis tothereby form a tilt angle 118 projected onto the y-z plane (sometimesreferred to here as γ). The tilt angle 118 determines the kinematicspeed ratio between the traction rings 102, 104. Each of the planets 108has a rotational velocity about the planet axis 106 and is shown in FIG.1A as planet velocity 122, sometimes referred to here as co. Typicallythe planet axis 106 corresponds structurally to a planet axle, which canbe operationally coupled to a carrier or a cage (not shown) that can bestationary, while in other embodiments the planet axle is coupled to acarrier (not shown) that is rotatable about main drive axis 152. In theplanet-centered coordinate system 160, the x-axis is directed into theplane of the page (though not shown precisely as such in FIG. 1A), andthe z-axis is generally parallel to the main drive axis 152. Forpurposes of illustration, the tilt angle 118 is generally defined in they_(g)-z_(g) plane.

Turning now to FIG. 1B, the planet-centered coordinate system 160 isresolved further to illustrate the angular adjustments of the planetaxis 106 that are used in the embodiments of skew control systemsdescribed here. As shown in FIG. 1B, a tilt angle 118 can be derived byrotating the coordinate system 160 with the planet axis 106 in the y-zplane about the x-axis to achieve a first relative coordinate system 170(x′, y′, z′). In the relative coordinate system 170, the planet axis 106coincides with the z′-axis. By rotating the coordinate system 170 withthe planet axis 106 about the y-axis, a skew angle 120 (sometimesreferred to here as ç) can be obtained in a x-z plane, which isillustrated by a second relative coordinate system 180 (x″, y″, z″). Theskew angle 120 can be considered, approximately, the projection in thex-z plane of the angular alignment of the planet axis 106. Morespecifically, however, the skew angle 120 is the angular position of theplanet axis 106 in the x′-z′ plane as defined by the relative coordinatesystems 170 and 180. In one embodiment of the CVT 100, the tilt angle118 is controlled, at least in part, through an adjustment of the skewangle 120.

Referring now to FIG. 1C, certain kinematic relationships betweencontacting components of the CVT 100 will be described to explain howthe inducement of a skew condition generates forces that tend to adjustthe tilt angle 118. As used here, the phrase “skew condition” refers toan arrangement of the planet axis 106 relative to the main drive axis152 such that a non-zero skew angle 120 exists. Hence, reference to“inducement of a skew condition” implies an inducement of the planetaxis 106 to align at a non-zero skew angle 120. It should be noted thatin certain embodiments of the CVT 100 certain spin-induced forces alsoact on the traction planet 108. Spin is a phenomenon of tractioncontacts well known to those of ordinary skill in the relevanttechnology. For our immediate discussion, the effects of thespin-induced forces will be ignored. In the CVT 100, components contactthe traction planet 108 at three locations to form traction or frictioncontact areas. With reference to FIG. 1, the first ring 102 drives theplanet 108 at a contact 1, and the planet 108 transmits power to thesecond ring 104 at a contact 2. The traction sun 110 supports thetraction planet 108 at a contact 3. For discussion purposes, the threecontacts 1, 2, 3 are arranged in FIG. 1C to reflect a view of the x″-z″plane as seen from a reference above the CVT 100, or View A in FIG. 1A.Since the contact areas 1, 2, 3 are not coplanar, contact-centeredcoordinate systems are used in FIG. 1C so that the contact areas 1, 2, 3can be illustrated with the x″-z″ plane. Subscripts 1, 2, and 3 are usedto denote the specific contact area for contact-centered coordinatesystems. The z_(1,2,3)-axis are directed at the center of the tractionplanet 108.

Referring now to contact area 1 in FIG. 1C, the surface velocity of thefirst traction ring 102 is denoted in the negative x₁ direction by avector V_(r1) and the surface velocity of the planet 108 is representedby a vector V_(p1); the angle formed between the vectors V_(r1) andV_(p1) is approximately the skew angle 120. The resulting relativesurface velocity between the traction ring 102 and the traction planet108 is represented by a vector V_(r1/p). At the contact area 3 betweenthe traction planet 108 and the traction sun 110, the surface velocityof the traction sun 110 is represented by a vector V_(sv) and thesurface velocity of the traction planet 108 is represented by a vectorV_(ps); the angle formed between V_(sv) and V_(ps) is the skew angle120. The relative surface velocity between the traction planet 108 andthe traction sun 110 is represented by a vector V_(sv/p). Similarly, forcontact 2, the surface velocity of the traction planet 108 at thecontact area 2 is shown as a vector V_(p2) and the surface velocity ofthe second traction ring 104 is represented by a vector V_(r2); theangle formed between V_(p2) and V_(r2) is approximately the skew angle120; the relative surface velocity between the traction planet 108 andthe second traction ring 104 is the resultant vector V_(r2/p).

The kinematic relationships discussed above tend to generate forces atthe contacting components. FIG. 1D shows a generalized, representativetraction curve that can be applied at each of contact areas 1, 2, 3. Thegraph illustrates the relationship between the traction coefficient μand the relative velocity between contacting components. The tractioncoefficient μ is indicative of the capacity of the fluid to transmit aforce. The relative velocity, such as V_(r1/p), can be a function of theskew angle 120. The traction coefficient μ is the vector sum of thetraction coefficient in the x-direction μ_(x) and the tractioncoefficient in the y-direction μ_(y) at a contact area 1, 2, or 3. As ageneral matter, the traction coefficient μ is a function of the tractionfluid properties, the normal force at the contact area, and the velocityof the traction fluid in the contact area, among other things. For agiven traction fluid, the traction coefficient μ increases withincreasing relative velocities of components, until the tractioncoefficient μ reaches a maximum capacity after which the tractioncoefficient μ decays. Consequently, in the presence of a skew angle 120(that is, under a skew condition), forces are generated at the contactareas 1, 2, 3 around the traction planet 108 due to the kinematicconditions. Referring to FIGS. 1C and 1E, V_(r1/p) generates a tractionforce parallel to the V_(r1/p) with a component side force F_(s1).Increasing the skew angle 120 increases the V_(r1/p) and, thereby,increases the force F_(s1) according to the general relationship shownin FIG. 1D. The V_(sv/p) generates a force F_(ss), and similarly, theV_(r2/p) generates a force F_(s2). The forces F_(s1), F_(ss), and F_(s2)combine to create a net moment about the traction planet 108 in the y-zplane. More specifically, the summation of moments about the tractionroller 108 is ΣM=R*(F_(s1)+F_(s2)+F_(ss)), where R is the radius of thetraction roller 108, and the forces F_(s1), F_(s2), and F_(ss) are theresultant components of the contact forces in the y-z plane. The contactforces, some times referred to here as skew-induced forces, in the aboveequation are as follows: F_(s1)=μ_(y1)N₁, F_(s2)=μ_(y2)N₂,F_(ss)=μ_(ys)N₃, where N_(1,2,3) is the normal force at the respectivecontact area 1, 2, 3. Since the traction coefficient μ is a function ofrelative velocity between contacting components, the tractioncoefficients μ_(y1), μ_(y2), and μ_(ys) are consequently a function ofthe skew angle 120 as related by the kinematic relationship. Bydefinition, a moment is the acceleration of inertia; hence, in theembodiment illustrated here, the moment will generate a tilt angleacceleration {umlaut over (γ)}. Therefore, the rate of change of thetilt angle {dot over (γ)} is a function of the skew angle 120.

Turning now to FIG. 1F, a traction planet 108 is illustrated having atilt angle 118 equal to zero, which results in the planet axis ofrotation 106 being generally parallel (in the yg-zg plane) to the maindrive axis 152 of the CVT 100 and the rotational velocity 122 of thetraction planet 108 is coaxial with the z-axis. A skew angle 120 can beformed in the x-z plane to generate forces for motivating a change inthe tilt angle 118. In the presence of the skew angle 120, the tractionplanet 108 would have a rotational velocity 122 about an axis z″, andthe tilt angle 118 would be formed in the y-z′ plane.

Passing now to FIGS. 2-17, embodiments of certain control systems for aCVT that rely on inducing a skew condition to motivate a change in thetilt angle 118 will be described now. FIG. 2 shows a drive 25 thatincludes a CVT 300 operationally coupled between a prime mover 50 and aload 75. The drive 25 can also include a skew-based control system 200.Typically, the prime mover 50 delivers power to the CVT 300, and the CVT300 delivers power to a load 75. The prime mover 50 can be one or moreof various power generating devices, and the load 75 can be one or moreof various driven devices or components. Examples of the prime mover 50include, but are not limited to, human power, internal combustionengines, electric motors and the like. Examples of loads include, butare not limited to, drivetrain differential assemblies, power take-offassemblies, generator assemblies, pump assemblies, and the like. In someembodiments, the skew control system 200 can coordinate the operation ofthe CVT 300 as well as the prime mover 50, or can coordinate theoperation of the CVT 300 and the load 75, or can coordinate theoperation of all elements in the drive 25. In the embodiment illustratedin FIG. 2, the skew control system 200 can be configured to use anadjustment of a skew angle 120 to control the operating condition of theCVT 300, and consequently, coordinate the control of the drive 25.

Referring now to FIGS. 3-5B, in one embodiment, a CVT 500 includes anumber of substantially spherical traction planets 508 configured tocontact a traction sun 510. The traction planets 508 can also contact afirst traction ring 502 and a second traction ring 504. The tractionrings 502, 504 can be arranged in a substantially similar manner as thefirst traction ring 102 and the second traction ring 104 depicted inFIG. 1A. The areas of contact between the traction planet 508, the firsttraction ring 502, the second traction ring 504, and the traction sun510 are substantially similar to contacts 1, 2, and 3, respectively,depicted in FIGS. 1A-1F. Likewise, the contact-centered coordinatesystems and the kinematic relationships discussed in reference to FIGS.1A-1F can be applied to the CVT 500 for descriptive purposes.

In one embodiment, a global coordinate system 550 (that is, x_(g),y_(g), z_(g)) is defined with reference to FIG. 3. The global coordinatesystem 550 is substantially similar to the global coordinate system 150.The global coordinate system 550 is generally oriented with respect to alongitudinal axis or a main drive axis 552 of the CVT 500, for examplewith the z_(g)-axis coinciding with the main drive axis 552 about whichthe traction planets 508 are arranged. The y_(g)-axis is perpendicularto the main drive axis 552. The x_(g)-axis is perpendicular to the maindrive axis 552. Each of the traction planets 508 has an axis ofrotation, that is, a planet axis 506, which can be configured to tilt inthe y_(g)-z_(g) plane to thereby form a tilt angle 511 (γ), which issubstantially similar to the tilt angle 118 (FIG. 1A). The planet axis506 can be configured to follow a first guide 512 (depicted as a line inFIG. 3) on one end of the planet axis 506. The planet axis 506 can beconfigured to follow a second guide 514 (depicted as a line in FIG. 3)on a second end of the planet axis 506.

Referencing FIG. 4 specifically, in one embodiment, the first guide 512and the second guide 514 can be formed on a first stator plate 516 and asecond stator plate 518, respectively. Typically the planet axis 506corresponds structurally to a planet axle, which can be operationallycoupled to the first and second guides 512, 514, respectively. In someembodiments, the first and second stator plates 516, 518 aresubstantially disc-shaped bodies configured to operably couple to and tofacilitate the support of the planet axis 506 during operation of theCVT 500. As an illustrative example for discussion purposes, the viewdepicted in FIG. 4 is of a projection of the stator plate 516 on thestator plate 518 in the x_(g)-y_(g) plane. An angular displacement 520of the stator plate 516 with respect to the stator plate 518 can bedefined in the x_(g)-y_(g) plane (the z_(g)-axis coinciding with themain drive axis 552 is perpendicular to the plane of the page of FIG. 4;the x_(g)-axis and the y-_(g) axis are each perpendicular to the maindrive axis 552). The angular displacement 520 is sometimes referred tohere as “angle β” or more succinctly as “β”. A skew angle, such as theskew angle 120, can be defined for the CVT 500 in a substantiallysimilar manner with respect to substantially similar coordinate systemsas those used in reference to the CVT 100. Therefore, the skew angle 120(ç) will be used here in reference to the CVT 500. A “zero-skew anglecondition” is defined as that condition of the planet axis 506 when theskew angle 120 is zero (ç=0).

Turning to FIG. 5A, the first and second guides 512, 514 are depictedagain as projections in the x_(g)-y_(g) plane. In some embodiments, thefirst guide 512 can be radially aligned with the origin of thex_(g)-y_(g) plane; for example, the first guide 512 can generallycoincide with the y_(g)-axis. In one embodiment, the second guide 514can have an offset 522 from the origin of the x_(g)-y_(g) plane. In oneinstance, the offset 522 can be generally defined as a linear offsetrelative to a construction line 519, which construction line 519 isparallel to the second guide 514 and passes through the origin of thex_(g)-y_(g) plane when the stator 516 is located at a nominally zeroangular displacement 520 (β). In a second instance, the second guide 514can have a base angular reference position 523 (Ψ_(o)) with respect tothe first guide 512.

Referring to FIGS. 5A and 5B, the guides 512 and 514 are depicted againschematically. In one embodiment, the stator 518 can be rotated to anon-zero angular displacement 520 (β), which moves the guide 514relative to the guide 512 (FIG. 5B). The offset 522 can be depicted as aradial offset 525 about the center of the stator 518 (that is, theorigin of the x_(g)-y_(g) plane). The guide 514 is tangent to the radialoffset 525. Referencing FIG. 5A specifically, the base angular referenceposition 523 (Ψ_(o)) with respect to the guide 512 is defined at a zeroangular displacement 520 (β=0) and a zero tilt angle 511 (γ=0). Thecorresponding zero-skew angle condition for the planet axis 506 isdepicted at a location 524, which lays at the intersection of the firstand second guides 512 and 514 when viewed as projections in thex_(g)-y_(g) plane. Referencing FIG. 5B specifically now, for a non-zeroangular displacement 520 (β), the guide 514 has an angular position 526(Ψ) with respect to the guide 512. The corresponding zero-skew anglecondition for the planet axis 506 is depicted at a location 527, whichis located at the intersection between the guide 512 and the guide 514when viewed as projections in the x_(g)-y_(g) plane. The location 527 isan example of a zero skew angle condition for a non-zero angulardisplacement 520 (β) and a non-zero tilt angle 511 (γ). It should benoted that the guides 512, 514 illustrated here schematically can beprovided, as will be illustrated below with regard to certainembodiments, as slots formed on stators 516, 518. In such instances, theguides 512, 514 can be representative of center lines that pass througha center of respective radial and offset slots. Schematically, as shownin FIGS. 5A-5C, a point of contact between a slot of a stator and aplanet axle (or a roller on such a planet axle) of the ball 508 has beenreduced to a point lying on one of the schematic guides 512, 514.However, in certain physical embodiments of the stator 516, 518, saidpoint of contact does not lie on a radial line.

A non-zero skew angle 120 (ç) can be induced on the planet axis 506 bytwo events, occurring separately or in combination. One event is achange in the angular displacement 520 (β), and the other event is achange in the tilt angle 511 (γ). In one embodiment, the relationshipbetween the angular displacement 520 (β) and the skew angle 120 (ç) fora constant tilt angle 511 (γ) depends on the geometry of the CVT 500,such as the length of the planet axis 506, and/or the radius of thestators 516, 518, among other factors. In one embodiment, therelationship between the angular displacement 520 (β) and the skew angle120 (ç) for a constant tilt angle 511 (γ) is approximately expressed bythe equation β=ç, for small angles. The relationship between the angulardisplacement 520 (β) and the angular position 526 (Ψ) can depend on thegeometry of the CVT 500 and the base angular reference position 523(Ψ_(o)), for example. In one embodiment, the angular position 526 (Ψ)can be proportional to the angular displacement 520 (β), so that therelationship can be approximated by the relationship Ψ=β+Ψ_(o), forsmall angles. For a constant angular displacement 520 (β), the skewangle 120 (ç) can also be related to the tilt angle 511 (γ). Forexample, the skew angle 120 (ç) can be related to the angular position526 (Ψ) and a change in the tilt angle 511 (delta γ) by the relationshiptan(ç)=(½*sin (delta γ)*tan(Ψ)). Applying the well known small angleapproximation to said expression yields the equation ç=½*(delta γ)*Ψ.

During operation of the CVT 500, the first and/or second stator plates516, 518 can be rotated to the angular displacement 520 via a suitablecontrol input (not shown in FIGS. 3-5C, but see FIG. 7 for an exemplarycontrol input). In some embodiments, the first stator plate 516 can beconfigured to be substantially non-rotatable with respect to the maindrive axis 552. The angular displacement 520 initially induces a skewangle 120 on the planet axis 506. As previously discussed, the skewangle 120 motivates a change in the tilt angle 511 (γ) of the planetaxis 506. As the planet axis 506 tilts, the ends of the planet axis 506follow the first and second guides 512, 514. The guides 512, 514 areconfigured so that the skew angle 120 decreases in magnitude as theplanet axis 506 tilts towards an equilibrium condition, which, in onceinstance, corresponds to a zero-skew angle condition. Once the planetaxis 506 reaches the tilt angle 511 (γ), which generally coincides witha zero-skew angle condition, the tilting of the planet axis 506 stops.In one embodiment, the tilt angle 511 (γ) of the planet axis 506depends, at least in part, on the angular displacement 520 (β). In someembodiments, the relationship of the tilt angle 511 (γ) and the angulardisplacement 520 (β) is unique, so that each value of the angulardisplacement 520 (β) corresponds to a value of the tilt angle 511 (γ) atwhich the CVT 500 can operate at an equilibrium speed ratio condition.

Upon reaching the equilibrium condition, each of the planet axes 506 issubstantially at a zero-skew angle condition. Since the planet axes 506,and consequently the traction planets 508, of the CVT 500 areindependently coupled to the stators 516, 518, each of the tractionplanets 508 and the planet axes 506 can independently self stabilize atthe equilibrium speed ratio condition. To elucidate further, when thetilt angle 511 (γ) of one of the planet axes 506 moves away from theequilibrium condition (for example, due to an outside influence or aperturbation in the operating condition), the ends of the planet axis506 follow the guides 512, 514. As previously discussed, a skewcondition is induced on the planet axis 506, and therefore, the planetaxis 506 tends to tilt toward the tilt angle 511 (γ) that generallycorresponds to the equilibrium condition for a given angulardisplacement 520 (β). The guides 512, 514 independently guide themovement or tilting of the planet axes 506. Therefore, the movement ortilting of one of the planet axes 506 can occur substantiallyindependently from the other planet axles of the CVT 500.

The configuration of the guides 512, 514 affects the ability of the CVT500 to stabilize at an equilibrium condition. For a given direction ofrotation of the first traction ring 504, the arrangement of the guides512, 514 depicted in FIG. 5A results in stable operation of the CVT 500.For example, a desired speed ratio can be maintained for the CVT 500that corresponds to the angular displacement 520 (β). Adhering to thesign convention generally defined in reference to FIGS. 1A-1F, it can beshown that, for a given angular displacement 520 (β), a positive changein the tilt angle 511 (γ) induces a positive change in the skew angleand vice versa. Therefore, each planet axis 506 can operate stably whenprovided with the relative arrangement of the guides 512, 514 depictedin FIG. 5A.

Referencing FIG. 5C now, in one embodiment, a guide 5121 and a guide5141 can be substantially similar in function to the guides 512, 514;however, the guides 5121, 5141 are arranged with a base angularreference position 5231 that is substantially opposite in direction(that is, the opposite sign) to the base angular reference position 523(Ψ_(o)) with respect to the x_(g)-y_(g) plane. Assuming the equivalentdirection of rotation of the first ring 504, and consequently thedirection of rotation of the traction planet 508, the arrangement of theguides 5121, 5141 could in at least some instances result in an unstableoperation of the CVT 500. For example, a desired speed ratiocorresponding to the angular displacement 520 (β) cannot be maintainedfor the CVT 500 because a positive change in the tilt angle 511 (γ)induces a negative skew angle and vice versa. Therefore a perturbationin operation that tilts one of the planet axes 506 will cause the planetaxis 506 to tilt until limited by, for example, a mechanical stop (notshown).

Referring now to FIG. 6A, in one embodiment a skew-based control process600 can be implemented on, for example, a microprocessor incommunication with power electronics hardware coupled to the CVT 500.The skew-based control process 600 begins at a state 602. The skew-basedcontrol process 600 then proceeds to a state 604, wherein a desiredspeed ratio (SR) set point of the CVT 500 is received. The skew-basedcontrol process 600 continues to a state 606 where the angulardisplacement 520 of, for example, the first stator 516 is determined.Next, the skew-based control process 600 moves to an actuator subprocess608 where the angular displacement 520 is applied to the stator 516, forexample. Upon completion of the actuator subprocess 608, the skew-basedcontrol process 600 proceeds to a state 609 where the actual SR of theCVT 500 is measured. In one embodiment, the actual SR of the CVT 500 canbe determined by measuring the speed of, for example, the traction rings502 and 504, or any other component indicative of input speed and outputspeed to the CVT 500. In some embodiments, the actual SR can becalculated based at least in part on a target output speed condition orbased at least in part on a target input speed condition. In otherembodiments, the actual SR of the CVT 500 can be determined by measuringthe tilt angle of the planet axis 506. In yet other embodiments, theactual SR of the CVT 500 can be determined by measuring an actual torqueratio of the CVT 500. The actual torque ratio of the CVT 500 can bedetermined by measuring the torque of, for example the traction rings502 and 504, or any other component indicative of input torque andoutput torque to the CVT 500. Next, the skew-based control process 600proceeds to a decision state 610 where the measured speed ratio iscompared to the desired speed ratio set point to thereby form acomparison value. If the measured speed ratio is not equal to thedesired speed ratio set point, the skew-based control process 600returns to the state 606. If the measured speed ratio is equal to thedesired speed ratio set point, the skew-based control process 600proceeds to an end state 612. In some embodiments, the skew-basedcontrol process 600 is configured to operate in an open loop manner; insuch a case, the states 609 and 610 are not included in the subprocess608.

Referring to FIG. 6B, in one embodiment the state 606 can use a look-uptable that can be represented by a curve 607. The curve 607 depicts anexemplary relationship between the angular displacement 520 (β) and thespeed ratio of, for example, the CVT 500. The curve 607 can be expressedby the equation y=Ax²−Bx+C, where y is the angular displacement 520 (β)and x is the speed ratio. In one embodiment, the values of A, B, and Care 0.5962, −4.1645, and 3.536, respectively. In some embodiments, thevalues of A, B, and C are 0.5304, −4.0838, and 3.507, respectively. Inother embodiments, the values of A, B, and C are related to thedimensions and geometry of the CVT 500, for example, the position ofguides 512 and 514 on the stators 516 and 518, the length of the planetaxis 506, and dimensions of the traction rings 502 and 504, among otherthings. In some embodiments, that actuator subprocess 608 is configuredto operate in an open loop manner; in such a case, the states 619 and620 are not included in the subprocess 608.

Referring to FIG. 6C, in one embodiment the actuator subprocess 608 canbegin at a state 614 and proceed to a state 615 where a set point forthe angular displacement 520 (β) is received. The actuator subprocess608 proceeds to a state 616 where an actuator command signal isdetermined based at least in part on the angular displacement 520 (β).In one embodiment, a look-up table can be used to convert the angulardisplacement 520 (β) set point to an actuator command signal. In someembodiments, the actuator command signal can be a voltage or a current.In other embodiments, the actuator command signal can be a change in theposition of a cable or a linkage. In some embodiments, an algorithm canbe used to derive the actuator command signal from the angulardisplacement 520 (β) set point. Next, the actuator subprocess 608proceeds to a state 617 where the actuator command signal is sent to anactuator and associated hardware. In one embodiment, a standard serialcommunication protocol can be used to send the command signal to theactuator hardware. In some embodiments, a cable or a linkage can be usedto transmit the command signal to the actuator hardware. The actuatorsubprocess 608 then passes to a state 618 where the stator, for examplethe stator 516, is rotated. Next, the actuator subprocess 608 passes toa state 619 where the angular displacement 520 (β) is measured. Theactuator subprocess 608 then proceeds to a decision state 620 where themeasured angular displacement 520 (β) is compared to the set point forthe angular displacement 520 (β). If the measured angular displacement520 (β) is not equal to the angular displacement 520 (β) set point, theactuator subprocess 608 returns to the state 616. If the measuredangular displacement 520 (β) is equal to the angular displacement 520(β) set point, the actuator subprocess 608 then ends at a state 622,wherein the skew-based control process 600 can continue at state 609 asdescribed above with reference to FIG. 6A. In some embodiments, theactuator subprocess 608 is configured to operate in an open loop manner;in such a case, the states 619 and 620 are not included in thesubprocess 608.

Passing now to FIG. 7, in one embodiment a CVT 1000 can include askew-based control system 1002 operably coupled to a variator assembly1004. In one embodiment, the variator assembly 1004 includes a tractionsun 1006 located radially inward of, and in contact with, a number ofsubstantially spherical traction planets 1008. The traction sun 1006 canbe configured to rotate about a main axle 1010 by providing bearings1011. In one embodiment, the traction sun 1006 is fixed axially withrespect to the main axle 1010 with clips 1012 that are coupled to themain axle 1010 and to the bearings 1011.

In one embodiment, each traction planet 1008 is provided with a set ofplanet axles 1009A and 1009B that are configured to provide a tiltableaxis of rotation for their respective traction planet 1008. The planetaxles 1009A and 1009B can be configured to rotate with the tractionplanet 1008. The planet axles 1009A and 1009B are substantially alignedwith a central axis the traction planet 1008. In other embodiments, thetraction planet 1008 can be configured to have a central bore, and thetraction planet 1008 can be operably coupled to a planet axle (notshown) via bearings, so that the planet axle is configured to besubstantially non-rotatable. Each of the traction planets 1008 areoperably coupled to a first stator 1014 and a second stator 1016. Thefirst and second stators 1014, 1016 can be arranged coaxial with themain axle 1010.

In one embodiment of the CVT 1000, an input driver 1018 can be arrangedcoaxial with the main axle 1010. The input driver 1018 can be configuredto receive an input power from, for example, a sprocket, a pulley, orother suitable coupling. In one embodiment, the input driver 1018 iscoupled to a torsion plate 1019 that is coupled to a first axial forcegenerator assembly 1020. The axial force generator assembly 1020 isoperably coupled to a first traction ring 1022 that can be substantiallysimilar in function to the traction ring 102 (FIG. 1A). The firsttraction ring 1022 is configured to contact each of the traction planets1008. A second traction ring 1024 is configured to contact each of thetraction planets 1008. The second traction ring 1024 can besubstantially similar in function to the traction ring 104 (FIG. 1A). Inone embodiment, the second traction ring 1024 is coupled to a secondaxial force generator assembly 1026. The second axial force generatorassembly 1026 can be substantially similar to the first axial forcegenerator assembly 1020. In certain embodiments, the axial forcegenerator assemblies 1020 and 1026 can be substantially similar to theclamping force generator mechanisms generally described in PatentCooperation Treaty Application PCT/US2007/023315.

During operation of CVT 1000, an input power can be transferred to theinput driver 1018 via, for example, a sprocket. The input driver 1018can transfer power to the first axial force generator 1020 via thetorsion plate 1019. The first axial force generator 1020 can transferpower to the traction planets 1008 via a traction or friction interfacebetween the first traction ring 1022 and the each of the tractionplanets 1008. The traction planets 1008 deliver the power to a hub shell1028 via the second traction ring 1024 and the second axial forcegenerator 1026. A shift in the ratio of input speed to output speed, andconsequently, a shift in the ratio of input torque to output torque, isaccomplished by tilting the rotational axis of the traction planets1008. In one embodiment, the tilting of the rotational axis of thetraction planets 1008 is accomplished by rotating the first stator 1014,which can be substantially similar to the first stator 516 (FIGS. 4-5C).

Turning now to FIG. 8, in one embodiment a CVT 2000 can be substantiallysimilar to the CVT 1000. For description purposes, only the differencesbetween the CVT 1000 and the CVT 2000 will be described. In oneembodiment, the CVT 2000 includes a traction sun 2007 located radiallyinward of, and in contact with each of the traction planets 1008. Thetraction sun 2007 is a substantially cylindrical body that can be formedwith a v-shaped profile about the outer periphery of the body whenviewed in cross-section in the plane of the page of FIG. 8. The tractionsun 2007 can be configured to contact each of the traction planets 1008at a first and a second location 2008 and 2009, respectively. Thecontact-centered coordinate systems and the kinematic relationshipsdiscussed in reference to contact 3 (FIGS. 1A-1F) can be similarlyapplied to the contact locations 2008 and 2009. During operation of theCVT 2000, the traction sun 2007 is substantially axially fixed bybalancing axial forces at contact locations 2008 and 2009. Further, insome embodiments, the first and second rings 1022, 1024 are configuredto provide sufficient radial kinematic constraint to the planets 1008;in such embodiments, the traction sun 2007 and bearings 1011 can beremoved from various embodiments of CVTs discussed here.

Referring to FIG. 9, in one embodiment the skew-based control system1002 can include a lever arm 1030 that can be configured to couple to astator driver 1032. The stator driver 1032 can be coupled to the firststator plate 1014 via, for example, a number of dowels or other suitablefasteners or couplings (not shown). In one embodiment the stator driver1032 can be a generally hollow cylindrical body. The stator driver 1032can be provided on one end with a flange 1031 that is configured tofacilitate the coupling of the stator driver 1032 to the first statorplate 1014. The stator driver 1032 can be provided with a groove thatcan be configured to receive a clip 1035 for retaining a bearing, forexample.

In one embodiment, the first stator plate 1014 can be configured torotate with respect to the main axle 1010. For example, a bushing 1033can couple to the first stator plate 1014 and to the stator driver 1032.The bushing 1033 can be arranged coaxial about the main axle 1010. Inone embodiment, a nut 1034 can be configured to cooperate with the mainaxle 1010 to axially retain the bushing 1033. In some embodiments, thesecond stator plate 1016 can be coupled to the main axle 1010 via aspline 1035, or other suitable torque transferring coupling, so that thesecond stator plate 1016 is substantially non-rotatable with respect tothe main axle 1010.

During operation of the CVT 1000, the lever arm 1030 can be rotatedabout the main axle 1010 to thereby generate an angular rotation of thestator driver 1032 about the main axle 1010. The lever arm 1030 can berotated manually via a linkage or a cable (not shown). In someembodiments, the lever arm 1030 can be operably coupled to an electronicactuator (not shown) such as a DC motor or a servo actuator. In someembodiments, the lever arm 1030 can be operably coupled to a hydraulicactuator (not shown). In other embodiments, the stator driver 1032 canbe coupled directly to an actuator such as any of those aforementioned.The angular rotation of the stator driver 1032 imparts an angulardisplacement (β) to the first stator plate 1014 with respect to thesecond stator plate 1016. As described earlier in reference to the CVT500, the angular rotation of the first stator plate 1014 with respect tothe second stator plate 1016 can facilitate the tilting of therotational axis of the traction planets 1008.

Turning now to FIGS. 10-13, in one embodiment the first stator plate1014 can be a substantially disc-shaped body having a central bore. Insome embodiments, the first stator plate 1014 can be provided with a hub1036 formed about the central bore. The hub 1036 can be provided with anumber of holes 1038 that can facilitate the coupling of the firststator plate 1014 to the stator driver 1032. A number of radially offsetslots 1040 can be formed on a face of the first stator plate 1014. Theradially offset slots 1040 can be configured to facilitate support ofthe traction planets 1008 via contact with, for example, a number ofrollers 1042 (see FIG. 9) that are operably coupled to each of the ballaxles 1009. The second stator plate 1016 can be provided with a numberof radial slots 1044. The radial slots 1044 can be configured to coupleto the rollers 1042. FIG. 10 depicts an exemplary arrangement of theradially offset slots 1040 with respect to the radial slots 1044. Fordiscussion purposes, the global coordinates 1047 (FIG. 9) are applied tothe CVT 1000. Consequently, the radial slots 1044 can be viewed asprojections on the first stator plate 1014 in the x_(g)-y_(g) plane. Theradial slots 1044 are shown with dashed lines in FIG. 10.

Referencing FIGS. 11A and 11B specifically, in one embodiment, theradially offset slots 1040 and the radial slots 1044 have a width 1046.The width 1046 can be sized to accommodate the outer diameter of theroller 1042. In the embodiment illustrated in FIG. 10, the radial slots1044 are arranged about the second stator plate 1016 so that theradially offset slots 1040 do not align (that is, are offset) with theradial slots 1044, as seen in the projection of the radially offsetslots 1040 and the radial slots 1044 onto the x_(g)-y_(g) plane. Theamount of linear offset 1048 is depicted in FIG. 11 with reliance on thesection lines A-A and B-B. The section line A-A substantially bisectsone of the radially offset slots 1040, wherein the bisection issubstantially half of the width 1046. The section line B-B substantiallyaligns with the centerline of the first stator plate 1014. The sectionline B-B is a line that is perpendicular to the main drive axis z_(g)(FIG. 9). The section line A-A is a line that is parallel to the sectionline B-B. Alternatively, the radially offset slots 1040 can be shown tohave an angular offset 1049 by defining a construction line 1050 and acenterline 1051. The centerline 1051 can be constructed with respect toa diameter of the first stator plate 1014. The construction line 1050 isshown for convenience to be at a radial location coinciding with thecenter of the planet axle 1009 when the planet axle 1009 is at a tiltangle substantially equal to zero. The angular offset 1049 can bedefined as the angular displacement between the centerline 1051 and themiddle of the radially offset slots 1040 lying along the constructionline 1050, wherein the middle of the radially offset slot 1040 issubstantially half of the width 1046. In one embodiment, the angularoffset 1049 is in the range of about 0 degrees to 45-degrees. In someembodiments, the angular offset 1049 can be between 5- and 20-degrees,and preferably 8-, 9-, 10-, 11- or 12-degrees.

Referring now to FIGS. 12 and 13, in one embodiment the first statorplate 1014 can be provided with a shift stop extension 1052 arrangedabout the central bore. The first stator plate 1014 can be provided witha generally toroidal clearance cut 1054. The clearance cut 1054 can beformed on the face of the first stator plate 1014. The clearance cut1054 can have a generally curved profile when viewed in the plane of theFIG. 13. Likewise, a valley 1041 and/or a wall 1043 of the radiallyoffset slot 1040 can be provided with a generally curved profile whenviewed in the plane of FIG. 12. During operation of the CVT 1000, theradially offset slots 1040 guide the rollers 1042. The shift stopextension 1052 can provide a mechanical limit to the path of the rollers1042 in the radially offset slots 1040. In some embodiments, the shiftstop extension 1052 can be formed on a radially outward periphery of thefirst stator plate 1014.

Turning now to FIGS. 14 and 15, in one embodiment the second statorplate 1016 can be a generally disc-shaped body having a central bore1056. The central bore 1056 can be configured to facilitate the couplingof the second stator plate 1016 to the main axle 1010 with, forinstance, a spline, knurl, or weld. The radial slots 1044 can bearranged angularly about the central bore 1056. In some embodiments, theradial slots 1044 can extend on the second stator plate 1016 from near,or in the vicinity of, the periphery of the stator plate 1016 toward thecentral bore 1056. The radial slot 1044 can be provided with a curvedprofile when viewed in the plane of FIG. 15. In one embodiment, thesecond stator plate 1016 can be provided with a shift stop extension1057. The shift stop extension 1057 can be formed radially about, andextend axially from, the central bore 1056. The shift stop extension1057 can be configured substantially similar to the shift stop extension1052.

Turning now to FIGS. 16 and 17, in one embodiment the planet axle 1009can be provided with a groove 1070 configured to receive a clip 1072.The clip 1072 can facilitate the coupling of the roller 1042 to theplanet axle 1009. In one embodiment, a surface 1074 can be provided onthe planet axle 1009 to provide support for a bearing 1076. The bearing1076 can be configured to couple to an inner diameter of the roller1042. In some embodiments, the bearing 1076 is pressed into the roller1042. In other embodiments, the roller 1042 can be configured to receivea ball bearing 1077. A bearing surface 1078 can be provided on theplanet axle 1009 for facilitating the coupling of the bearing 1077 tothe planet axle 1009.

Referring still to FIGS. 16 and 17, in one embodiment the roller 1042 isa generally cylindrical body having a central bore. The central bore canbe configured to receive the bearing 1076 or the bearing 1077. Theroller 1042 can be provided with a crowned outer circumference of thecylindrical body. The crowned outer circumference is configured tofacilitate the coupling of the planet axle 1009 to the first and thesecond stator plates 1014 and 1016.

It should be noted that the description above has provided dimensionsfor certain components or subassemblies. The mentioned dimensions, orranges of dimensions, are provided in order to comply as best aspossible with certain legal requirements, such as best mode. However,the scope of the inventions described herein are to be determined solelyby the language of the claims, and consequently, none of the mentioneddimensions is to be considered limiting on the inventive embodiments,except in so far as any one claim makes a specified dimension, or rangeof thereof, a feature of the claim.

The foregoing description details certain embodiments of the invention.It will be appreciated, however, that no matter how detailed theforegoing appears in text, the invention can be practiced in many ways.As is also stated above, it should be noted that the use of particularterminology when describing certain features or aspects of the inventionshould not be taken to imply that the terminology is being re-definedherein to be restricted to including any specific characteristics of thefeatures or aspects of the invention with which that terminology isassociated.

What we claim is:
 1. A method of supporting a plurality of tractionplanets of a continuously variable transmission (CVT), each tractionplanet having a tiltable axis of rotation, the method comprising thesteps of: providing a first stator plate having a plurality of radiallyoffset slots, the radially offset slots arranged angularly about acenter of the first stator plate; operably coupling each of the tractionplanets to the first stator plate; providing a second stator platehaving a plurality of radial slots, the radial slots arranged angularlyabout the center of the second stator plate; and operably coupling thetraction planets to the second stator plate.
 2. The method of claim 1,wherein the first stator plate is configured to rotate relative to thesecond stator plate.
 3. The method of claim 1, wherein the first statorplate is substantially non-rotatable about a main drive axis of the CVT.4. The method of claim 1, wherein the second stator plate issubstantially non-rotatable about a main drive axis of the CVT.
 5. Themethod of claim 1, wherein a shift stop extension is located on thefirst stator plate, the shift stop extension arranged about a center ofthe first stator plate.
 6. The method of claim 5, wherein the shift stopextension is located radially inward of the radially offset slots. 7.The method of claim 5, wherein the shift stop extension is locatedradially outward of the radially offset slots.
 8. The method of claim 1,wherein the plurality of radially offset slots have a curved profile. 9.A stator plate for a continuously variable transmission (CVT) having aplurality of traction planets, the stator plate comprising: asubstantially disc shaped body having a center; and a plurality ofradially offset guides arranged angularly about the center, each of theradially offset guides having a linear offset from a centerline of thedisc shaped body.
 10. The stator plate of claim 9, further comprising ashift stop extension arranged about the center.
 11. The stator plate ofclaim 10, wherein the shift stop extension is located radially inward ofthe radially offset guides.
 12. The stator plate of claim 10, whereinthe shift stop extension is located radially outward of the radiallyoffset guides.
 13. The stator plate of claim 9, wherein the disc shapedbody is configured to be non-rotatable about the main drive axis of theCVT.
 14. The stator plate of claim 9, wherein the disc shaped body isconfigured to be rotatable about the main drive axis of the CVT.
 15. Thestator plate of claim 9, wherein the radially offset guides have acurved profile.
 16. The stator plate of claim 9, wherein a valley and/ora wall of the radially offset guides has a curved profile.
 17. Thestator plate of claim 9, wherein each of the radially offset guides hasa linear offset from a centerline of the disc shaped body such that afirst line (A-A) is parallel but not aligning with a second line (B-B),wherein the first line (A-A) substantially bisects one of the radiallyoffset guides, and wherein the second line (B-B) is perpendicular to amain drive axis (z_(g)) of the CVT.
 18. The stator plate of claim 17,wherein the bisection of the first line (A-A) is substantially half thewidth of one radially offset guide.